The flexibility and attractive economics of RIM has created intense interest in the development of improved RIM processes within the industry and also in the development of RIM processible polymeric materials, including both improved urethane/urea and non-urethane/urea formulations. Inasmuch as the performance of polymeric materials produced by RIM is sensitive to the molding or processing conditions, the proper screening and evaluation of new RIM processed materials requires molding or processing under commercially realistic conditions. The smallest commercial RIM equipment currently available requires seven to ten liters of each monomer component in order to produce a single test specimen. In a research environment, the preparation of such large amounts of monomer is time consuming and expensive. There is accordingly an important need for a laboratory scale RIM apparatus capable of operating comparably to existing commercial RIM apparatus, but which only requires a comparatively small amount of each monomer component, say for example, one liter.
RIM requires the simultaneous injection under pressure of precisely controlled quantities of two or more monomer components into a mixing head fitted to a mold, whereby the pressurized components are mixed and then directed into the mold cavity. Among the problems encountered heretofore, no apparatus has been available for delivering the separate monomers to the mixing head in comparatively small, precisely proportioned quantities. Even when the supply lines for the RIM apparatus are initially filled with the monomers to be molded various time consuming interactions, feedback reactions, and mechanical play or lost motion between linkages in conventional RIM apparatus require the delivery of a minimum of several liters of each of the pressurized monomers into the RIM apparatus to obtain the steady flow rates and molding pressure required for precisely proportioned delivery of each monomer into the mold cavity.
It is accordingly an important object of the invention to provide an improved method and apparatus for achieving realistic commercial RIM processing conditions while requiring comparatively small amounts of each monomer for a complete molding operation. The term "monomer" as used herein means any fluid chemical formulation capable of reacting with one or more other monomers in a RIM apparatus.
Another important object is to provide improved apparatus for delivering two or more monomers to a RIM mixing head in precisely predetermined proportions, and which is readily adjustable for varying the proportions in any desired relationship.
In accordance with a more specific object, a longitudinally extensible lever pivotally mounted at one end for swinging about the axis of a fixed pivot is operatively connected with the piston rod of a primary piston and cylinder assembly. Hydraulic fluid is supplied at a metered rate to the primary cylinder to drive the piston therein and swing the lever about the fixed pivot. Each of two or more hydraulic driven piston and cylinder assemblies has a piston rod connected with a driven piston for discharging hydraulic fluid from the associated cylinder. Each driven piston is also operatively connected with the extensible swinging lever at a predetermined position spaced from the fixed pivot along the length of the lever, such that the connected driven piston is moved to discharge hydraulic fluid from the associated cylinder at a rate proportional to the distance of the fixed pivot from the operative connection of the piston rod with the lever.
A separate driven piston and cylinder assembly is provided for each component monomer required for the resulting RIM polymer and at least one is an adjustable driven assembly moveable bodily with respect to the axes of the fixed pivot and cylinders of the other driven assemblies to enable adjustable spacing of its operative connection with the lever and thereby to enable adjustment of the ratio of hydraulic fluid discharged from the cylinder of the adjustable driven assembly with respect to the cylinders of the other driven assemblies.
The hydraulic fluid discharged from the cylinder of each driven assembly is conducted into a corresponding hydraulic lance drive cylinder for driving a lance piston therein at a rate proportional to the rate that such fluid is discharged from the driven assembly. A lance connected with each lance piston and of smaller cross sectional area extends in sealing relationship from the lance drive cylinder into a component delivery cylinder for amplifying the pressure of fluid monomer component within the delivery cylinder and also for discharging the component therefrom at the amplified pressure into the supply conduit for the mold cavity and at a rate proportional to the rate of travel of the lance piston.
Another important object is to provide a hydraulic connection between each driven assembly and each lance drive cylinder, whereby simple valve switching means can be employed to connect the cylinder of any driven assembly with any lance drive cylinder. Thus in a two component RIM system for example, hydraulic fluid can be supplied selectively to either lance drive cylinder in ratios ranging from 1:1 to 1:0. Such versatility of operation is especially desirable under laboratory conditions where monomer components A and B for a first test polymer might be required in a 5:6 ratio and in a 6:5 ratio for a second test polymer. Without the provision of the valve switching means, in order to deliver component A in the smaller proportion for the first test polymer and thereafter in the higher ratio for the second test polymer, it would be necessary either to provide the component delivery cylinders with replaceable sleeves to change their relative cross sectional areas, or to clean the component delivery cylinders thoroughly and thereafter interchange the component monomers in the two delivery cylinders. Thorough cleaning is emphasized because if some of monomer A remains that is intended to be replaced in the delivery cylinder by monomer B, the resulting reaction will spoil the test sample and possibly clog the supply lines in the RIM apparatus.
The several component delivery cylinders, one for each monomer required for the molded polymer, are each initially filled completely with the monomer to be discharged therefrom. Likewise all of the hydraulic cylinders and connecting lines are completely filled. The various connections between the pistons and their connecting rods are preferably rigid, the various pivotal connections required are manufactured to close tolerances to eliminate play or lost motion in the associated connections, and a comparatively conventional non-compressibile hydraulic fluid is employed in the hydraulic circuits. Accordingly the lance drive and component delivery cylinders may be located closely to the mold, independently of the location of the ratio proportioning fluid delivery cylinders, assuring a minimum length of component supply lines to the mold.
The close tolerances in the few connections involved, the pressure magnification obtained by the use of the lances for forcing the monomers from the component delivery cylinders into the supply conduits to the mold cavity, and the elimination of various factors noted above and responsible for increasing the time required and consequent wasted monomer before attainment of operature pressure, say 2000 psi (pounds per square inch) to possibly 3500 psi, enable an almost instant build-up of pressure and flow rate to operating conditions in the short component supply lines employed and rendered feasible by the arrangement described. In fact, the primary delay in attainment of operating pressure results from the inevitable swelling of the pressurized component delivery system as the high operating pressure is reached. Such swelling and the quantity of unuseable components in the supply lines is further minimized by using small steel, say half-inch, diameter supply lines.
Inasmuch as mixing of the monomers is critical in order to obtain uniform RIM polymer test samples, a commercial mix head is preferred. All in all, an inventory of approximately 300 cc at most of each monomer is required to fill the lines to the mold, which inventory cannot be used to make a polymer. A mixing head valve, referred to herein as a wipe piston, is employed to prevent flow of the monomers into the mold until the steady state flow rate at the desired molding pressure is obtained. An initial liter of each monomer will thus provide 700 cc of useable monomer, sufficient to produce essentially ten 4".times.8".times.0.125" polymer plaques for testing.
When a predetermined steady pressure and flow rate are obtained in the lines to the mold, the valve closing the mold entry is opened and the pressurized monomers rush into the mixing head, then into an after mixer which may comprise part of the mold and which affects additional mixing, and then into the mold where the molding operation is completed in accordance with conventional practice.
Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.